The present invention relates generally to a solid state depth locator or "fish finder" having a liquid crystal display (LCD), and more particularly, to a depth locator wherein the LCD is driven in real time and wherein the darkness of individual LCD segments may be varied.
Depth locators or fish finders have been used in the fishing industry for providing a user with a generalized "picture" of what is in the water under a boat or other vessel, based on the return signals produced in response to sonar transmissions into the water. Non-solid state depth locators having motors, rotating neon bulbs and other moving parts are less reliable, noisy and high in power consumption. Solid state depth locators having LED indicators are also high in power consumption. Liquid crystal displays have been used in connection with depth locators in the fishing industry to overcome these problems.
In the past, depth locators systems having LCD's use multiplexers to drive the individual segments of the LCD at a rate fast enough to be flicker free. The advantage of driving the LCD segments with multiplexers is a reduction in the number of chips necessary to drive the LCD which reduces the cost of the system. However, the disadvantages of a multiplexer driven LCD include a narrow viewing angle such that the user must be generally right over the display in order for it to be seen clearly. Also, LCD's driven by multiplexers require the use of microprocessors having inherent processing times which cause an event lag and prevent the display from being in real time.
In addition, depth locator systems utilizing LCD's typically implemented only two LCD states: an "on" state when an LCD segment was polarized indicating the presence of a target, and an "off" state when the LCD segment was not polarized indicating the absence of a target. Some of these systems produce grey areas which are the result of a checkerboard arrangement in which some segments are "always on" and in which some segments are "always off".
Thus, in addition to providing a system which eliminates the viewing angle, event lag, and the direct sun-light bleeding out or fading problems, it would be desirable to provide a system capable of grey scaling individual LCD segments for indicating the relative strength of a target.